I. Field of the Invention
The present invention relates to alternating current welding systems and, more particularly, to a high frequency welding system having pincer jaws adapted to clampingly engage the work therebetween.
II. Description of the Prior Art
In the manufacture of automobiles, aircraft and industrial equipment, resistive welding is extensively used throughout the manufacturing process. These previously known devices typically comprise a pair of the pincer fingers which clampingly engage opposite sides of the work with one finger on each side of the work. Electric current in the range of 50-60 hertz is then conducted through the fingers, and thus through the work, thereby forming the weld.
One disadvantage of utilizing resistive welding systems with the electric power supplies at 50-60 hertz is that relatively large and heavy transformers are required in order to supply current to the pincer fingers.
The use of higher welding frequencies, for example 400 hertz, would effectively reduce the size, cost and weight of the transformers necessary to electically couple the pincer fingers to the electrical power source. For the reasons discussed below, however, the use of such higher frequencies has been heretofore impractical.
More specifically, for many applications, each pincer finger comprises an elongated shank having a welding tip at one end. Thus, when the welding tips on the pincer fingers clampingly engage the work, the metal sandwiched in between the two pincer fingers acts like a transformer core. Consequently, when a high frequency electrical power source is applied to the pincer fingers, a great deal of energy is lost to the magnetic field caused by current flow through the pincer fingers which is inductively imparted to the metal clamped or positioned between the fingers.
For example, assuming a transformer of 20,000 A RMS and a welding gun having pincer arms 16 inches long, at 60 hertz of current, approximately 16,000 A RMS of current is applied to the weld while only 4,000 A RMS of power is lost to the magnetic field induced in the work. Conversely, with the same welding gun operated at 400 hertz, only about 3,000 A RMS is applied to the weld while the remaining 17,000 A RMS is lost to inductive field induced in the work. For this reason, high frequency welding systems have not heretofore been extensively employed in such heavy manufacture operations.